Process for manufacturing thermoplastic sheet and apparatus therefor

ABSTRACT

In an apparatus and process for manufacturing a thermoplastic sheet or film having superior optical characteristics such as improved transparency, gloss and surface smoothness, a thermoplastic sheet is extruded, passed between a cast drum and an endless metallic belt while being compressed and subjected to a primary cooling by the belt and drum. The sheet or film is secondarily cooled in a water bath, after which it is dewatered and subjected to a thermal treatment at a temperature in the range of 40° C. below, to 15° C. above the thermal deformation temperature of the resin sheet to produce the improved sheet of the invention. In addition to producing a film or sheet with improved characteristics, the apparatus of the invention allows production of sheets or films at a rate up to about 10 m/min.

TECHNICAL FIELD

The present invention relates to a process for manufacturing athermoplastic sheet or film and an apparatus therefore, which may beoptimally used in various industrial applications to provide a packagefor foodstuffs, stationery document files etc., and various packagingcases.

BACKGROUND ART

The thermoplastic sheet, such as, for example, a crystallinethermoplastic sheet (or a film) is used extensively in variousindustrial applications, by virtue of its superior characteristics suchas heat resistance, various physical properties, chemical resistance andhinging characteristics.

However, neither a process for making a crystalline thermoplastic sheetof improved transparency, gloss and surface flatness nor a technologyfor making such a sheet at a high-speed has been developed andavailable.

Known processes for manufacturing the crystalline thermoplastic sheetinclude the air-knife process, the polishing-roll process, thewater-cooling process and the like.

In the air-knife process, it may be difficult to maintain a surfaceflatness since the film upon which an air is sprayed may be variable,which is caused by a step of tightly urging the film-like fusedthermoplastic resin against the cast drum under an air pressure to beinjected from the nozzle. Besides, one side of the sheet cannot becooled rapidly because it is cooled by air. Consequently, the processhas a drawback in that it may not produce a sheet of improvedtransparency, surface flatness and thickness precision etc. Urgingforces by an air pressure has approximately a 3000 mm water column asits upper limit, and a production speed of approximately 20 m/minute isa maximum for producing a commercially valuable sheet or film, becausethe air is directed only at a single point. As a result, this air-knifeprocess is mainly used to make a reduced thickness sheet ofapproximately 0.2-0.5 mm which would not need particular appearancecharacteristics. However, this process is not suitable to produce anincreased thickness sheet of approximately 0.7 mm or more.

The polishing-roll process is a method for producing a sheet by forcinga film-wise fused thermoplastic resin between a pair of metallic rolls.In this process, the sheet thickness and the surface configuration areimposed simultaneously at a point where a pair of rolls contact eachother, and if a drawing-speed is reduced to an order of approximately 4m/min or less, a sheet of improved surface flatness may be produced.However, when the drawing speed is higher than approximately 6 m/min, asheet-forming step may not follow such a fast rate, and still produce acommercially usable sheet.

If the reduced thickness sheet of approximately 0.4 mm or less is madein accordance with the polishing-roll process, water's edge-like wavesare generated to prevent production of commercially usable sheets.

Many proposals have been made in the water-cooling process, and atypical example is found in Japanese Patent Application UnexaminedPublication No. Hei.4-158022. In this sheet manufacturing process, asheet-like fused crystalline thermoplastic resin is cooled andsolidified with water, and then re-heated by heating rollers, to befollowed by the step of forcing the sheet between a pair of metallicbelts such that its appearance characteristics and its production ratemay be improved. Though this process may provide a sheet with anincreased transparency, it may substantially compromise its appearancecharacteristics, since stripe-like patterns may be formed laterally inthe sheet when the action of the water's edge-like waves are imposedagainst the sheet while the fused resin is being cooled by water. Thegreater the sheet-withdrawal forces are, the more frequently suchpatterns may be formed.

On the other hand, while a non-crystalline thermoplastic sheet has beenmanufactured using a similar process, a sheet of improved gloss, andsurface roughness may not be successfully provided. Thus, an improvementin this aspect has been desired.

DISCLOSE OBJECTS OF THE INVENTION

A primary object of the present invention is to provide a process and anapparatus therefore which may solve the above-described problems andpermit the manufacture of crystalline thermoplastic sheet or film ofsuperior appearance characteristics in transparency, gloss and surfaceflatness etc., at a high-speed, without requiring a special sheetthickness.

A second object of the present invention is to provide a process and anapparatus therefore which may permit the manufacture of non-crystallinethermoplastic sheets of superior gloss and surface flatness at ahigh-speed.

SUMMARY OF THE INVENTION

The process of the present invention for manufacturing the thermoplasticsheet includes the steps of introducing a fused thermoplastic resinwhich has been extruded in a sheet-like configuration from the T-die ofa T-die extruder into a clearance between a cast drum and an endlessbelt which is spaced from and opposes against the surface of the drum inan arcuate configuration with a predetermined clearance formedtherebetween, exposing the sheet-like fused resin to a primary coolingoperation to be effectuated in the temperature range covering a pointwhere the resin is thermally deformed and a point where it is softened,while forcing said sheet-like fused resin into a clearance between thecast drum and the endless metallic belt, then immediately introducingthe sheet which has been subjected to this primary cooling operationinto a cooling tank in which cooling water is held so that it may becooled secondarily to its solidification temperature, removing waterwhich has collected on the secondarily cooled sheet, and subsequentlythermally treating the sheet from which remaining water has been removedat a temperature range between 40° C. lower than the thermally deformingpoint and 15° C. higher than the above-described reference point.

The the apparatus of the present invention for manufacturing thethermoplastic sheet includes a T-die of the T-die extruder in which thethermoplastic resin may be fused and the fused resin is extruded in asheet-like configuration. Compressing and cooling means are arranged atthe downstream side of the T-die, and are adapted to expose thesheet-like fused resin from the T-die to a primary cooling operationwhile compressing the resin in a clearance between a cast drum and anendless metallic belt in a predetermined spacing from and opposingrelationship in an arcuate configuration with the drum surface. Acooling tank is arranged at the downstream side of the compressing andcooling means for secondarily cooling the sheet after its primarycooling step. Water removing means is arranged at the downstream side ofthe cooling tank for removing water off the sheet has been secondarilycooled, and thermally treating means which is arranged at the downstreamside of the remaining water removing means for improving quality of thesheet from which water has been removed as above-described by applyingheat. The metallic belt of the compressing and cooling means ispivotally supported in position by means of three first, second andthird metallic rolls, and the first metallic roll is positioned abovethe cast roll in a place most adjacent to the T-die, such that anopposing space between the cast drum and the metallic drum may be formedin an arcuate configuration between the first metallic roll and thesecond metallic roll.

In the meantime, the sheet of the present invention as described hereinincludes the film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating one example of the apparatus formaking the sheet built in accordance with the present invention.

The process and apparatus of the present invention will be described indetail hereinbelow.

In accordance with the present invention, it is possible to use acrystalline thermoplastic resin or a non-crystalline thermoplastic resinas a thermoplastic resin. As the crystalline resin, such materials maybe used as polyethylene resin, polypropylene resin, crystallinepolyester resin, and polyamide resin. A preferable material ispolypropylene resin. As the non-crystalline resin, such materials may besuggested as polystyrene resin, acrylonitrile-butadiene-styrene resin(ABS resin), polycarbonate resin, non-crystalline polyethyleneterephtalate resin (a-PET), vinylchloride resin and the like. Theseresins may be applied either as a mono-polymer, or a co-polymer incombination with other co-monomers, or alternatively its blend. In casethe material used is, for example, polypropylene resin, it is alsoavailable to use a crystalline propylene monomer, a crystallineco-polymer to be formed by polymerizing propylene with a plurality ofco-monomers such as, for example, ethylene, butene etc, other thanpropylene and its mixture.

It is also available to add, if desired, to the thermoplastic resin asabove-described such materials as anti-oxidant, lubricant, antistaticagent, slip agent, antiblocking agent, ultraviolet absorber, nucleusforming agent, transparency improver, organic peroxide, inorganic fillermaterial such as pigment, talc, and calcium carbonate, organic fillermaterial such as wood flour, synthetic fiber etc., and other resin orrubber (in the case of polypropylene resin, for example, polyethylene,polypropylene rubber and the like can be added).

Then, the process of the present invention will be describedhereinbelow, with reference to an apparatus illustrated in the drawing.

In FIG. 1, there are shown a T-die 1 in the T-die extruder, and athermoplastic resin which has been fused in the extruder (the main frameof which is not illustrated) and then extruded from the T-die 1 in asheet-like configuration. Arranged at the downstream side of the T-die 1is compressing and cooling means consisting of the cast drum 3 and theendless belt 4 which opposes against the surface of the drum in apredetermined clearance therebetween in an arcuate configuration. Themetallic belt 4 is pivotally supported in position by means of first,second and third metallic rolls 5, 6 and 7. These metallic rolls arepositioned in a place most adjacent to the T-die 1, thereby forming theopposing region of arcuate configuration, or the compressing and coolingportion 8 of the cast drum 3 and endless metallic belt 4 between thismetallic roll 5 and the second metallic roll 6.

The sheet-like fused resin 2 which has been extruded through the T-die 1is then introduced into a clearance between the cast drum 3 and theendless belt 4, that is, the compressing and cooling section 8, and thentransferred toward the second metallic roll 6, and thus the sheet-likefused resin 2 is exposed to the primary cooling operation while it isbeing compressed at the compressing and cooling section 8. In themeantime, it may be difficult and unnecessary to maintain a uniformclearance between the cast drum 3 and the metallic endless belt 4 alongthe entire span from the first metallic roll 5 to the second metallicroll 6 before the fused resin is introduced, since the metallic belt 4is flexible. Thus, it is only required that the belt portions againstwhich the first metallic roll 5 and the second metallic roll 6 may atleast contact respectively are preset at a predetermined value prior tointroduction of the fused resin. In other words, the above-describedclearance dimensions may be maintained to be uniform between the contactpoints (the metallic belt between the first metallic roll 5 and thesecond metallic roll 6) under a compressive stress to be imposed by thefused resin.

The clearance between the cast drum 3 and the endless belt 4 is designedto be adjustable by a mechanical adjustment in such a way that forexample, the cast drum 3 may be shifted upwardly or downwardly. Theseclearance dimensions correspond to a thickness to which the sheet 19 maydesirably be produced as a product. Consequently, the product sheetthickness may be eventually determined by presetting these clearancedimensions.

The primary cooling temperature to be achieved during the compressingand cooling operation represents a temperature range covering a pointwhere the thermoplastic resins are thermally deformed and a softeningpoint (that is, normally in the range of 90°-160° C. with polypropylene,for example ). (This testing procedure is in accordance with JIS K-6758,with the assumption that a load is 1 kgf.) When the primary coolingtemperature is lower than the above-described level at which a thermaldeformation may occur, the sheet with superior transparency and glossmay not be obtained. On the other hand, if the primary coolingtemperature exceeds the above-described softening point, the sheet willbecome too soft to impair its characteristics of releasing from the castdrum 3 and the metallic belt 4, resulting in a multiple of minutedefects on the sheet surface, or wrinkles may be produced on the sheetin a subsequent step of transferring the sheet into the cooling tank 10,and thereby interfering with the production of good quality products.

In the present invention, it is preferable to construct first and thirdmetallic rolls 5, 7 such that they may be heated from their internalsection, and the metallic belt 4 may be heated by these first and thirdmetallic rolls 5, 7 which have been thus heated from their internalsections. The heating temperature of this metallic belt with thepolypropylene resin usually has its surface temperature in the range of50°-150° C., for example. It is also preferable to construct the castdrum 3 to be heated from their internal sections in a similar manner.The heating temperature of the cast drum with the polypropylene resinusually has its surface temperature in the range of 50°-150° C., forexample.

Each of the metallic belts 4 is formed of SUS (stainless steel), carbonsteel, titanium alloy and the like, but a material SUS is preferred byvirtue of its greater corrosion inhibitive property etc. The cast drumand metallic rolls 5, 6 and 7 may be formed of carbon steel (with hardchrome plating applied over its surface), as in the case of prior art.

It is suitable to select the surface hardness of the cast drum 3 and themetallic belt 4 (at a surface where it may contact with theabove-described fused resin) to be less than 0.5 μm, and more preferablyto be less than 0.3 μm, when it is used to make a sheet with improvedappearance characteristics (that is, one having an improved transparencyand appearance characteristics when a crystalline thermoplastic resin isused, and one having an improved gloss and surface smoothness when anon-crystalline thermoplastic resin is used). Meanwhile, such cast drum3 or metallic belt 4 can provide the sheet-like fused resin with animproved transferability.

The cast drum 3 is not limited to the above-described surface roughnesswhen it is used to provide a product sheet upon which an emboss patternor a strip-like straight pattern is used, for example, and any suitablepattern may be provided suitably on the surface by applying asculpturing process and the like.

Since the metallic belt 4 is used as an endless belt to be jointed by awelding process, it is required that irregular configurations on thewelded portion may not impose any influence upon the sheet. In the caseof a reduced thickness metallic belt, such irregular configurations mayoccur easily at the joint portion, whereas a greater thickness metallicbelt may loose its flexibility and interfere with its intendedapplication. Thus, the metallic belt is suitably formed to have itsthickness in the range of 0.5-1.2 mm.

The first metallic roller 5 may preferably have a heat-resistant rubbersuch as a silicon rubber, or a resilient elastomer coated over itssurface when it is desired to provide a sheet having optically improvedcharacteristics without impairing its surface smoothnesscharacteristics. When an elastomer is used, the rubber hardness issuitably in the range of 55-85. In either case, the coating thickness issuitably in the range of 5-15 mm.

The sheet 9 which has been exposed to the primary cooling operation asabove-described is then immediately brought into a cooling tank 10 whichcontains a cooling water and is arranged at the downstream side of thecompressing and cooling means. Consequently, the sheet is exposed to asecond cooling operation where it is cooled to be solidified completely.The temperature of cooling water is suitably in the range of 0°-25° C.when a polypropylene sheet is treated, for example.

Then, the sheet 11 which has been exposed to a second cooling operationis guided to means 20 which is arranged at the downstream side of thecooling tank 10 for removing water, and cooling water which hascollected on the sheet 11 during the secondary cooling operation isremoved. The remaining water removing means may be formed in astraightforward construction which includes, for example, a pair ofpinch rolls 12, and an air blow device 13 which is arranged downstreamof the pinch rolls. In this case, remaining water on the sheet 11 issqueezed out through a pair of pinch rolls 12, and may be completelyremoved by an air spraying from the airblow device 13 (the air may becold or heated).

It is often experienced that the rigidity of the sheet 14 is reduced dueto a curling, or the resins are not crystallized adequately. Therefore,the present invention attempts to improve these characteristics throughthermal treatment. Thus, in the process of the present invention, thesheet 14 which has its remaining water removed is finally guided tothermal treating means 21 which is arranged at the downstream side ofthe remaining water removing means 20, and is exposed to the thermaltreatment so that the product sheet 19 may be provided which has desiredperformance characteristics.

The thermal treatment means 21 may be formed in a straightforwardconstruction in which it includes, for example, a plural number (in thiscase, four, for example) of heated metallic rollers 15, 16, 17 and 18(each of which is constructed to be heated internally by means ofheating oil etc.) or an oven.

The heating temperature covers a range of 40° C. lower than the thermaldeformation point of the thermoplastic resin (more preferably a point of30° lower than the above-described thermal treating level) and a point15° C. higher than the thermally deformable level (more preferably 5° C.higher than the above-described thermally deforming temperature). (Thistemperature range normally covers 90°-150° C. when polypropylene istreated.) A substantial effect in modifying curled configuration andimproving rigidity may not be expected if it is lower than 40° C. lowerthan the thermal deformation level. Wrinkles and impaired appearancessuch as transparency and gloss may occur at a temperature 15° C. higherthan the thermal deformation point, because the sheet acquires a softcondition.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1!

The polypropylene sheet was manufactured using the apparatus as shown inFIG. 1.

The polypropylene resin used was a nitrogen polymer XF 1893 (a productname of polypropylene monomer available from Tisso Co., Ltd) withdensity 0.90 g/m³, melt-flow rate 1.8 g/10 minutes, thermal deformationtemperature 90° C., and softening temperature of 130° C. This resin wasmelted in the T-die extruder (the extruder cylinder diameter 100 mm,L/D=36, the die width 550 mm, and the die lip clearance 1.2 mm)(components other than the T-die not shown), and was extruded throughthe T-die 1 in a sheet-like configuration. This sheet-like fused resinwas then introduced into a clearance between the cast drum 3 and theendless metallic belt 4, and was exposed to a primary cooling operationwhile it was being compressed, and it was then immediately guided to thecooling tank to effectuate a secondary cooling operation. Afterremaining water was subsequently removed through the pinch-roll 11 andthe air-blow device 13, the polypropylene sheet of 0.3 mm thickness wasmade by applying a thermal treatment procedure to heat metallic rolls15, 16, 17 and 18.

The particulars and sheet manufacturing conditions were as describedbelow;

Metallic Belt: SUS

Cast Drum

Carbon Steel with Hard Chrome Plated Surface, Width: 650 mm, SurfaceRoughness: 0.3 μm,

Surface Temperature: 90° C.

First Metallic Roll

Silicon Rubber of 65 Rubber Hardness Coated Over the Surface inThickness 10 mm.

Arcuate Compressing and Cooling Section

Length: 60 cm.

Clearance between Cast Drum and Metallic Belt: 0.3 mm

Sheet Withdrawal Speed

10 m/min (Rotating speed of the cast drum and the travelling speed ofthe metallic belt were both 10 m/min.)

Primary Sheet Cooling Temperature 110° C.

Water Tank

Length: 4 m,

Cooling Water Temperature: 10° C.

Air-Blow Device

Blow Air Temperature: 80° C.

Thermally Treatment Means (Heating Metallic Roll Group)

Material: Carbon Steel with Hard Chrome-plated Surface

Upstreammost Roll 15 Temperature: 60° C.

Downstreammost Roll 18 Temperature: 50° C.

Intermediate Rolls 16, 17 Temperature Between Above-described Rolls:100° C.

Surface Roughness of these Metallic Rolls: 1.0 μm

The polypropylene sheet which was made as above-described had haze(transparency) 3.4%, gloss 114% and superior surface smoothness with nostreaks, wrinkles and water's edge-like waves etc., and so it hadsuperior optical characteristics and appearance, with a high Young'sModule (Rigidity) of 94.

Meanwhile, the methods for measuring the thermally deforming temperatureand the softening temperature were as described below.

Thermally Deforming Temperature: JIS K-7207 (Load 4.6 kgf/c)

Softening Temperature: JIS K-6758 (Vicar Softening Point, Load 1.0 kgf)

Melt Flow Rate: JIS K-6758 (230° C., Load 2.16 kgf)

Density: JIS K-6758

Haze: ASTM D-1003

Gloss: ASTM D-523

Young's Module: ASTM D-882

Surface Smoothness: Visual Inspection

Streaks, Wrinkles, Water's Edges: Visual Inspection

Embodiment 2!

A polypropylene sheet of 0.5 mm in thickness was made using the sameprocess as that of the Embodiment 1, except that the clearance betweenthe cast drum and the metallic belt was selected to be 0.5 mm.

This sheet had superior characteristics substantially comparable tothose in the Embodiment 1. That is, the sheet had a superior surfacesmoothness, i.e., haze (transparency) 4.0% and a gloss 124%. Besides,since no streaks, wrinkles and water's edge-like surface etc., takeplace, optical characteristics and appearance were improved, providing ahigh Young's Module (rigidity) of 90.

Embodiment 3!

A polypropylene sheet of 1.0 mm thickness was produced in accordancewith the same manufacturing process as that employed in Embodiment 1,except that a clearance between the cast drum and the metallic belt waspreset to be 1.0 mm.

This sheet also showed improved characteristics substantially the samewith those in the Embodiment 1, that is, the sheet was superior in itssurface smoothness, showing a haze (transparency) 9.5% and a gloss 127%.Since no streaks, wrinkles and water's edge-like wavy surface etc., takeplace, it had improved optical characteristics and appearances. Itshowed a high Young's Module (Rigidity) of 88.

Embodiment 4!

A polypropylene sheet of 0.3 mm thickness was produced in accordancewith the same procedure as that used in the Embodiment 1, except thatthe cast drum, the first metallic drum and the thermal treating meanswere modified as below.

Cast Drum: Emboss Pattern Formed On the Surface

First Metallic Roll: No Surface Coating Layer

Thermal Treatment Means (Metallic Rolls Group)

Intermediate Rolls 16, 17 Surface Temperature: 80° C.

The embossed sheet displayed superior optical characteristics of haze3.6%, gloss 121% and the Young's Module 85.

Comparison I!

A polypropylene sheet of 0.3 mm thickness was produced using the samemanufacturing process as that used in a Embodiment 1, except that themetallic rolls in a thermal treating means, i.e., downstreammost andupstreammost metallic rolls were made to have equal surfacetemperatures, and the intermediate metallic roll had the surfacetemperature of 130° C. The sheet had the haze of 11.5%, gloss 86% andthe Young's Module 90. The sheet was verified to be inferior to one asobtained in respective embodiments, showing a poor surface smoothnessand wrinkles on the sheet surface.

Possibility for Industrial Utilization

In accordance with the present invention, a thermoplastic sheet or filmmay be provided which has superior optical characteristics such astransparency and gloss etc, appearance characteristics such as surfacesmoothness etc, and rigidity and the like, when a crystallinethermoplastic resin is used. On the other hand, when a non-crystallinethermoplastic resin is used, a thermoplastic sheet or film may beprovided which has superior optical characteristics such as gloss etc,appearance characteristics such as surface smoothness etc, and rigidityand the like. Either of these sheets or films may be embossed asdesired. Furthermore, it is also possible to make a high quality productwith a reduced or increased thickness sheet or film. Additionally, theproduction speed can be made several times faster than that available inthe prior process. The process and the device of the present inventionmay be also applied in the production of multi-layered sheet orlaminated sheet.

Consequently, the sheet or the film which may be obtained using thepresent invention may be usably utilized in packaging foodstuff, drugs,packaging case for cosmetics and household articles and industrial rawmaterials.

I claim:
 1. A process for manufacturing a thermoplastic sheet, whereinsaid process comprises the steps of:introducing a fused thermoplasticresin which has been extruded from a T-die in a T-die extruder in asheet-like configuration into a clearance between an outer surface of acast dram and a metallic endless belt which opposes said drum surfacewith a predetermined spacing therebetween in an arcuate configuration;cooling the fused resin of sheet-like configuration in a primary coolingoperation in a temperature range covering a thermal deformation point ofsaid resin and a softening point of said resin, while compressing saidsheet-like fused resin between the cast drum surface and the endlessbelt; introducing the sheet which has been subject to a primary coolingimmediately into a cooling tank having cooling water so as tosecondarily cool the resin to at least its solidifying temperature;removing cooling water which has collected on the secondarily cooledsheet; and thermally treating said secondarily cooled sheet in atemperature range between a point about 40° C. lower than the thermaldeformation temperature and a point about 15° C. higher than the thermaldeformation point.
 2. The process as claimed in claim 1, wherein thethermoplastic resin is a polypropylene resin.
 3. The process as claimedin claim 2, wherein the primary cooling temperature is in the range90°-100° C., and the thermally treating temperature is in the range90°-150°.
 4. The process as claimed in claim 2, wherein the secondarycooling temperature is in the range 0°-25° C.
 5. The process as claimedin claim 2, wherein the primary cooling temperature is achieved bymaintaining the temperature of a first metallic roller, about which saidbelt rotates and which is adjacent to said cast drum and said T-die, ata temperature in the range of 50°-150° C., and by maintaining thetemperature of the cast drum surface at a temperature in the range of50°-150° C.
 6. An apparatus for manufacturing a thermoplastic resincomprisinga T-die in a T-die extruder to fuse a thermoplastic resin andextrude the fused resin into a sheet-like configuration; compressing andprimary cooling means which is arranged at the downstream side of theT-die for cooling said sheet-like fused resin from the T-die in aprimary cooling operation while compressing said sheet-like fused resinbetween a surface of a cast dram and a metallic endless belt whichopposes the drum surface with a predetermined clearance therebetween inan arcuate configuration; a cooling tank downstream of the compressingand primary cooling means for immediately secondarily cooling the resinsheet which has been subject to the primary cooling, said tankcontaining cooling water; means downstream of said cooling tank forremoving cooling water from the secondarily cooled sheet, and thermaltreating means downstream of said water removing means for heating thesheet from which the collected water has been removed so as to improvethe performance characteristics of the resin, wherein said metallic beltis pivotally supported in position by first, second and third rollers,and said first roller lies above the cast dram and adjacent to the T-dieand said second metallic roller lies a distance from said first metallicroller and adjacent to said cast drum so as to enable said belt to forma spacing in an arcuate configuration.
 7. The apparatus as claimed inclaim 6, wherein said metallic belt is formed of a material selectedfrom the group consisting of SUS, carbon steel and titanium alloy. 8.The apparatus as claimed in claim 6, wherein the first metallic rollerhas its surface coated with a material selected from the groupconsisting of a heat-resistant rubber and a resilient elastomer.
 9. Theapparatus as claimed in claim 6, wherein the cast drum, the firstmetallic roller and the third metallic roller are heated by an internalheating means.
 10. The apparatus as claimed in claim 6, wherein the castdrum and the metallic belt have the surface roughness of less than 0.5mm.
 11. The apparatus as claimed in claim 6, wherein the cast drumsurface is embossed.
 12. The apparatus as claimed in claim 6, whereinthe metallic belt has the thickness in the range of 0.5-1.2 mm.
 13. Theapparatus as claimed in claim 6, wherein said water removing meansconsists of a pair of pinch rolls and an air blow device which isdownstream of the pinch rolls.
 14. The apparatus as claimed in claim 6,wherein said thermal treating means consists of a plurality of heatedmetallic rollers.
 15. The apparatus as claimed in claim 6, wherein saidthermal treating means includes a plurality of metallic rollers in aheating oven.